Phosphonic diesters are esters of phosphonic acid [HP(O)(OH)2], which is tautomeric with phosphorous acid [P(OH)3]. The phosphonic diesters are frequently referred to, not entirely correctly, as secondary phosphates. Nevertheless the true derivatives of phosphorous acid are only the triesters.
Diphosphonic diesters are the diesters of the diphosphonic acid:(HO)(O)PH—O—PH(O)(OH),which formerly was also referred to as diphosphorous acid(cf. in this regard Römpp Lexikon der Chemie, Georg Thieme Verlag, Stuttgart, N.Y., 1990, “Phosphites”, “Phosphonates”, “Phosphonic acid”, “Diethyl phosphite”, and “Dimethyl phosphite”).
Curable mixtures, especially coating materials, particularly clearcoat materials, which comprise polyester binders are known to be used in automotive OEM finishing since they produce thermally cured mixtures, especially coatings, particularly clearcoats, which have surfaces with an outstanding overall appearance. In laminates comprising at least one substrate, at least one coating, at least one adhesive layer, and at least one sheet, however, they leave something to be desired in their adhesion effect.
International patent application WO 03/011992 proposes improving the adhesion in multicoat paint systems through the use of carbinol-functional siloxanes which have been reacted with boric acid. Coupling agents of that kind, however, are surface-active, and so interact with other additives, especially silicone additives, and so impair the flow of the coatings.
Specifically in the context of automotive finishes the American patent application US 2005/0074617 describes the use of silane-containing acrylate copolymers which in addition may also contain hydroxyl groups. A strong interaction or influence of the silane groups on or with other functional groups, especially hydroxyl groups, is described. These interactions entail restrictions to the degrees of freedom affecting the resin synthesis and/or affecting the formulation of clearcoat materials for automotive OEM finishing.
The use of silane-containing coupling agents is indeed known in the prior art—see, for example, German patent applications DE 100 51 485 A1, DE 28 09 588 A or DE 25 59 259 A or the international patent application WO 2005/105938—but the action of these substances alone, without additional activators, is limited and is inadequate especially for particular applications in the field of polyester-containing two-component clearcoat materials for automotive OEM finishing.
German patent application DE 10 2005 045 228.0-44, unpublished at the priority date of the present specification, describes how silane-containing mixtures are able, with suitable additions based on phosphonic acid derivatives, to form particularly stable three-dimensional networks as reaction products. The coupling agent utility is not described.
The object on which the present invention is based is to find new coupling agents, especially new coupling agents for laminates comprising at least one substrate, at least one coating, at least one adhesive layer, and at least one sheet, which no longer have the disadvantages of the prior art.
The new coupling agents ought to produce outstanding adhesion within the coatings, so that when laminates comprising at least one substrate, at least one coating, at least one adhesive layer, and at least one sheet are subjected to mechanical load there is no delamination between substrate and coating, within the coating, or between coating and adhesive layer, but instead only a cohesive fracture within the adhesive layer.
The new coupling agents ought also to allow the simple and precisely reproducible production of laminates comprising at least one substrate, at least one coating, at least one adhesive layer, and at least one sheet.
Furthermore, the new coupling agents ought to be suitable for producing thermally curable mixtures, especially coating materials, particularly clearcoat materials, which are stable on storage and/or have a long pot life or processing life.
Not least the new thermally curable mixtures, especially the coating materials, particularly the clearcoat materials, ought to give cured materials, especially coatings, particularly clearcoats, which are particularly hard, abrasion-resistant, highly scratch-resistant, particularly chemical-resistant, and etch resistant, and which also, as clearcoats, are of particularly high gloss and clarity.
The new clearcoats ought in particular, as part of multicoat paint systems, to exhibit outstanding adhesion properties, so that in laminates comprising at least one substrate, at least one multicoat paint system with at least one new clearcoat, at least one adhesive layer, and at least one sheet the effect of mechanical load is accompanied only by cohesive fracture within the adhesive layer.